A and B, working together, take 15 days to complete a piece of work. If A alone can do this work in 18 days, then how long would B take to complete the same work?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 90 days.
A and B, working together, can complete the work = 15 days
The work rate of A and B together = 1/15
A alone can complete the work = 18 days
Therefore, A's work rate = 1/18
The work rate of B = work rate of A and B - work rate of A
⇒ 1/15 - 1/18 = (18 - 15)/270 = 3/270 = 1/90
Time taken by B = 1/Work rate of B = 90 days